Fluorescent discharge lamp and electrode therefor



Feb. 26, 1963 D. B. CLARK 3,079,521

FLUORESCENT DISCHARGE LAMP AND ELECTRODE THEREFOR Filed Dec. 14, 1960 FIG./.

INVENTOR. 001V 5; CLARK ATTORNEY involving delicate electrical measurements.

3,079,521 FLUORESQENT DESCHARGE LAMP AND ELECTRGDE THEREFOR Don B. Clark, tentura, Califi, assignor to the United States of America as represented by the Secretary of the Navy Filed Dec. 14, 1956, Ser. No. 75,893 3 Claims. (Cl. 313l61) (Granted under- Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of. America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to fluorescent lighting lamps and particularly to interference retarding hot cathodes or electrodes for such lamps.

It is well known that fluorescent lamps, as ordinarily used in lighting circuits, are sources of radio interference, electrical noise, and electrical disturbances that are inimical to efiicient communications and experimentation While not precisely determined, it is believed that the source of such interference may be due to the formation of a cathode spot on some arbitrary portion of the usual transverse filament. The plasma thus forms at these spots in a nonsymmetrical fashion with a random natural oscillation occurring at the cathodes during the conduction of current through the ionized gases enclosed in the lamp tube.

Recognizing the over-all efiiciency and economy of the fluorescent type of lighting, various attempts have been made to overcome this objectionable radio interference by providing expensive and cumbersome line filtering and -various forms of bonded shielding. Such attempts have been generally either unsuccessful or uneconomical.

The principal object of this invention, therefore, is to provide improved anode and cathode electrodes for fluorescent lamps whereby the flow of the plasma therein and thereabout may be controlled so as to reduce, if not eliminate, the radio interference and electrical disturbances usually associated with such lighting devices.

Another object of the invention is to provide an improved fluorescent lamp which is interchangeable with the standard lamps and fixtures now furnished.

Other objects and advantages of my invention will be appreciated in connection with the following detailed description and drawings wherein:

FIGURE 1 is a schematic view of a standard fluorescent tube bearin g my improved electrodes;

FIG. 2 is a schematic view, pa tly in section, illustrating one end of the tube shown in FIG. 1 with one electrode;

FIG. 3 is an enlarged elevation of my improved electrode;

FIG. 4 is a partial plan view of the electrode shown in FIG. 3; and

FIG. 5 is a detailed view of the filament used in my improved electrode.

With reference to FIGS. 1 and 2, the usual glass or quartz phosphor coated tube 19 is provided with my improved electrodes 12 and 14 sealed therein. Tube is evacuated and then filled with the necessary gases under low pressures, such as mercury vapor in combination with argon or neon, as is customary in the manufacture of such fluorescent lamps. Leads 13 and 15 are provided to provide filament current for starting and then operating current for lighting in the usual manner. The ends of the tube It) may be provided with enlarged portions or buttons 16 which support the leads 13 and 15 and insulate them from each other.

With reference to FIGS. 3, 4, and 5, the electrode structure comprises the double-coiled filament 13, a supporting 3,h79,52t l atented Feb. 26, 19%3 plate 22, a metallic post 2 and two control rods 25 and 26.

The metal supporting plate 22 may be rectangular, oblong, or circular in shape with a thickness sulficient to be embedded in or otherwise adhesively secured to the rounded top of button 16 and support the centrally disposed metal post 24 and the parallel control rods 25 and 26. The longitudinal axis of post 2 is generally concentric to the longitudinal axis of the tube It}. The longitudinal axes of the control rods are parallel to the tube axis and are disposed equidistant from that of the post 24, all three axes being preferably disposed in a plane. Post 24 ice is provided with a transverse slit 27 near its upper end for receiving the central bight of the filament wire and thus making an electrical connection between the post and the central portion of the filament. After the insertion of the filament wire into the slit 27, it may be closed by a slight tap on the top of the post 24. Other forms of electrical connection could be used, such as welding, but the method 'escribed has been found most desirable.

Control rods 25 and 26 are preferably constructed from a hollow stock of paramagnetic material; a portion of a No. 26 hypodermic syringe needle has been found to be ideal for this purpose. The outer ends of these hollow control rods may be filled with the electron emitter material that is used in conjunction with the filament. These rods are inserted in holes formed in support plate 22 and are brazed or otherwise secured electrically to the plate. As indicated previously, these control rods are parallel to each other, to the post 24, and are preferably equidistant from the central post. While shown with a sharp tip or point, these control rods may be supplied with a blunt point, particularly when the smaller gauges of hollow stock are used.

The filament 18 is similar to that found in standard fluorescent lamps and may consist of a 3 mil. tungsten wire 19 first wound on a 7 mil mandrel. This coiled wire is then wound on a 40 mil mandrel. In the preferred form of my invention, this second coil will be 12 or 13 turns. By pulling on the middle coil, two sections of 6 turns each are formed with one turn being pulled out to make the central bridge connection to post 24. The first coil 21% is placed upwardly over the control rod 25 and the second coil 21 is placed downwardly over control rod 26. The central bridge connection is then electrically connected to post 24 and the outward ends of the filament coils are electrically connected to the inward ends of the leads 15. Thus, as current flows through the filament 18, the magnetic flux induced in rod 25 flows in one direction while that induced in rod 25 flows in the other direction.

After the filament 18 is secured in place between the leads i5 and post 24, it may then be covered with a paste electron emitter material 28 such as barium carbonate or other suitable material. The prepared filament-electrode structures may then be inserted into the ends of tube 19 and the remainder of the construction of the fluorescent lamp follows standard practice.

It should be noted here that the filament is divided electrically and physically to allow operation of my improved lamp in standard circuits regardless of how it is inserted in the holder socket and that the electrode structure, rods 25, 25, and post 24, are connected only through post 24 to the center of the filament.

While the principles of operation are somewhat complex and not fully understood as yet, it would appear that the filament coils 2t and 21 are oriented physically and electrically to provide a symmetrical longitudinal magnetic field to guide and control the flow of plasma in the cathode and anode areas. This generated longitudinal magnetic field is such as to be degenerate to natural oscillations of the plasma and tends to spread the plasma out in 3 a symmetrical fashion so that no hot spots are formed on the filamentary material. The function of the control rod is not only to provide intensification and direction to the magnetic field produced by the coiled filament segment but to'allow tube current to flow through it and the filament in a reverse direction (negative feed back) whereby the natural oscillations occurring in the tube ionic current flow are reduced and/ or eliminated.

Having thus described my invention, I claim: 1. An improved fluorescent lamp including: an open-ended tube of transparent material with a coating .ofi fluorescent phosphor on its inner wall and havin'g a longitudinal axis parallel to said inner wall; a quantity of mercury vapor and argon at low pressures contained within said tube; an improved'electrode structure mounted at each end of said tube, said improved electrode structure comprising: an insulating end plug hermetically sealed in each of the open ends of said tube; a pair of electrical contact leads passing through said end plug and being parallel to saidlongitudinal axis; a double coiled filament supported by said pair of leads in the interior of said fluorescent tube, said filament consisting of two separate electrically connected vcoiled segments each of said coiled segments having a longitudinal axis parallel to the longitudinal axis of the other coiled segment and parallel to thelongitudinal axis of said tube;

electron emitting material surrounding said filaments for transforming said mercury vapor and argon into an ionized plasma; and

paramagnetic means associated withsaid longitudinally coiled filament segments for creating a magnetic field for controlling the distribution and natural oscillations of said plasma.

2. An improved fluorescent lamp comprising:

.a fluorescent-coated tube containing gases capable of ionization at low pressures and conduction of current :at low-voltages, and having a longitudinal axis;

hermetically sealed end plugs for said tube;

a pair of contact leads protruding interiorly and exteriorly of each said end plug, said leads being sub- ,stantially parallel to the longitudinal axis of said tube;

a double coiled filament supported by each pair of leads in the interior of said tube, said filament-consistingof two separate electrically connected coiled segments, each of said coiled segments having a longitudinal axis parallel to the longitudinal axis of the other coiled segment and parallel to the longitudinal axis of said tube;

electron emitting material carried by said filament for transforming said gases into an ionized plasma;

a hollow magnetic core for each of said coiled segments, the axes ofsaid cores being parallel to each other and the longitudinal axis oftsaid tube; and

meansfor electrically connecting each of said magnetic cores substantially to the center of the electrical connection between said'coiled segments of said filament.

3. An improved electrode for a fluorescent lamp having a longitudinal axis:

a pair of electrical contact'leads supported at an end of said fluorescent lamp leading from the exterior into the interiorof said lamp;

a transverse supporting plate of magneticmaterial supported between said leads in the interior of said lamp;

a post of magnetic material centrally disposed with relation to saidplate and said contact leads, said post being supported by said plate coaxially with the longitudinal axis of said lamp;

a pair of hollow magnetic controlrods supported by said plate equidistant from and parallel to said post; a double coiledfilament supported by and between said contact leads in the interior of said lamp, said filament consisting of two separate electrically connect-ed coiled segments, each of'said segments surrounding one of said control rods; an electrical connection between said post and-the electrical center of said filament;and a quantity of electron emitter materialsurrounding said filament and contained in each of the hollow interior ends of'saidcontrol rods.

References Cited inthe file of this patent IED TA E BATE T 

1. AN IMPROVED FLUOROSCENT LAMP INCLUDING: AN OPEN-ENDED TUBE OF TRANSPARENT MATERIAL WITH A COATING OF FLUORESCENT PHOSPHOR ON ITS INNER WALL AND HAVING A LONGITUDINAL AXIS PARALLEL TO SAID INNER WALL; A QUANTITY OF MERCURY VAPOR AND ARGON AT LOW PRESSURES CONTAINED WITHIN SAID TUBE; AN IMPROVED ELECTRODE STRUCTURE MOUNTED AT EACH END OF SAID TUBE, SAID IMPROVED ELECTRODE STRUCTURE COMPRISING: AN INSULATING END PLUG HERMETICALLY SEALED IN EACH OF THE OPEN ENDS OF SAID TUBE; A PAIR OF ELECTRICAL CONTACT LEADS PASSING THROUGH SAID END PLUG AND BEING PARALLEL TO SAID LONGITUDINAL AXIS; A DOUBLE COILED FILAMENT SUPPORTED BY SAID PAIR OF LEADS IN THE INTERIOR OF SAID FLUOROSCENT TUBE, SAID FILAMENT CONSISTING OF TWO SEPARATE ELECTRICALLY CONNECTED COILED SEGMENTS EACH OF SAID COILED SEGMENTS HAVING A LONGITUDINAL AXIS PARALLEL TO THE LONGITUDINAL AXIS OF THE OTHER COILED SEGMENT AND PARALLEL TO THE LONGITUDINAL AXIS OF SAID TUBE; ELECTRON EMITTING MATERIAL SURROUNDING SAID FILAMENTS FOR TRANSFORMING SAID MERCURY VAPOR AND ARGON INTO AN IONIZED PLASMA; AND PARAMAGNETIC MEANS ASSOCIATED WITH SAID LONGITUDINALLY COILED FILAMENT SEGMENTS FOR CREATING A MAGNETIC FIELD FOR CONTROLLING THE DISTRIBUTION AND NATURAL OSCILLATIONS OF SAID PLASMA. 